1. Field of the Invention
The present invention relates to reciprocating internal combustion engines in general, and more specifically, to engines equipped with heat recovery, heat recycle, and other heat conserving systems. The present invention also relates to a reciprocating internal combustion engine with reduced specific emissions of carbon dioxide, unburned hydrocarbons, carbon monoxide, and nitrogen oxides per unit of power produced.
2. Description of Prior Art
The internal combustion (IC) engine is well over 100 years old. The original US patent was issued to Nicolaus Otto on Aug. 14, 1877 for a four-stroke spark ignited (SI) engine. An earlier patent was issued to Otto for a four-stroke engine in Germany. A compression ignition (CI) engine, or Diesel engine, was invented a few years after this. Other than rotary engines, which were introduced many years later, internal combustion engines have powered our society and are found almost everywhere. These engines have primarily been both two and four stroke varieties.
Many improvements have been made to both the SI and CI engines over the years to improve their thermal efficiencies and to reduce their particulate emissions and noxious chemicals emissions, particularly unburned hydrocarbon (HC), carbon monoxide (CO), and mixed nitrogen oxides (NOx). Thermal efficiencies of spark ignited engines have increased over this time frame from single digits up to about 32% in everyday usage. One research study showed a thermal efficiency approaching 43% on a four-stroke SI engine fueled with and optimized for neat methanol (Matthew Brusstar, et al., “High Efficiency and Low Emissions from a Port-Injected Engine with Neat Alcohol Fuels”, SAE Paper 2002-01-2743, 2002). This high efficiency was made possible by modifying the engine to make use of the higher octane of alcohol compared to gasoline. The CI engines have achieved 52% to 57% thermal efficiency in large slow speed maritime applications such as the MAN S80ME-C7 with a specific fuel consumption of 156 to 168 g of fuel/KWh. These efficiencies are the peaks or maximums, not the average efficiencies. Engines are currently being developed which claim thermal efficiencies up to 60%, but these have not been commercialized. The ratio of weight to power output of IC engines has dropped over this same period, thus allowing their application in high power transportation demands all the way down to their use in hand tools and model airplanes.
A reciprocating internal combustion (IC) engine always includes one or more cylinders. Within each cylinder is a reciprocating piston connected to a crankshaft, which converts the reciprocating motion of the piston to a circular motion. Four strokes are performed in a conventional IC engine; these include the air or oxidizer intake stroke, compression stroke, power or combustion stroke, and the exhaust stroke. These form the complete cycle. Two stroke IC engines are also very common, but they are less efficient and emit more noxious chemicals than a four-stroke engine.
The main problems with internal combustion engines is the low thermal efficiency plus the release of particulates, unburned hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Thermal efficiency is the useful work output of an engine divided by the heat put into the engine, which is primarily fuel combusted at its lower heating value plus the heat entering with the air. The peak thermal efficiency for a SI engine is about 32% in an automotive application, but the thermal efficiency of the same engine at its normal operating point may be only 15 to 20% or lower. In the 20% thermal efficiency case, 80% of the heat energy entering is discarded as waste heat and is not converted to useful work. In a conventional engine, this heat is lost through the exhaust, through the walls of the engine, and through the cooling system, whether the engine is air cooled or liquid cooled. Friction inside the engine also accounts for 10 to 25% of the gross work output from the engine. This friction ends up as heat exiting the engine, so this friction is already included in the peak efficiency figures. There are ways of increasing the thermal efficiency of an engine, but in each case, there are tradeoffs. Increasing the compression ratio of an engine can raise engine efficiencies, but this is limited by the combustion characteristics of the fuel. Air-to-fuel ratios can also be varied. In this case, less than stoichiometric fuel can be utilized; meaning that excess air is present. Combustion in this case produced too much NOx in the exhaust. NOx is a result of high temperature combustion when combined with high levels of nitrogen and some oxygen. Lower temperature combustion coupled with less nitrogen would drastically reduce or essentially eliminate the formation of NOx. Combustion can also be greater than stoichiometric, thus producing an exhaust with particulates, unburned hydrocarbons (HC), and carbon monoxide (CO). In present day SI engines, the air-to-fuel ratio must be stoichiometric for the current after-treatment catalysts to give emissions which meet or exceed government mandates.
There are other ways of increasing the thermal efficiency of IC engines. These have included turbocharging, supercharging, recycling the heat, double or triple reduction of exhaust pressure, port fuel injection, direct fuel injection, homogeneous charge compression ignition, and other ignition regimes. Work is on-going on variable valve timing, camless valve operation, and cylinder deactivation to name a few. These have increased and are increasing thermal efficiencies but these improvements need to occur at a more rapid rate. A paradigm shift in thermal efficiency and a reduction in emissions are needed and both are provided by this invention.
There have been many variations of the four-stroke IC engine in an effort to improve the thermal efficiency. Others have recognized this deficiency in the four-stroke engine and have made steps to recover and recycle this heat. These efforts have resulted in increasing the number of strokes from four to six or eight or more. In a six stroke engine, strokes one through four generally include oxidizer intake, compression, power or combustion, and exhaust as in a conventional four-stroke engine. Strokes five and six and less frequently strokes three and four vary depending on the invention and the goal of the inventor. A fluid, either water, air, or steam is injected in stroke five to recover some of the heat remaining in the cylinder, piston, and cylinder head. This fluid is expanded or vaporized from the heat remaining in the metal of the cylinder, piston, and cylinder head and is thus pressurized without additional fuel being consumed. In the case of water being added, this water is vaporized to steam with its pressure dependent on the temperature and heat contained in the metal of the cylinder, piston, and cylinder head. This produces an additional power stroke without the introduction of additional fuel. Hot water is sometimes used rather than cold water and this allows the pressure developed during stroke five to be greater and thus to generate more work. Stroke six is the exhaust stroke to remove either the vaporized water or heated fluid from the cylinder before repeating the oxidizer intake stroke. There are, of course, other variations of this theme but all give a second power stroke within the six strokes of the engine.
There are many examples of six stroke engines in the patent literature. There are also examples in the patent literature of the use of steam and water inside combustion chambers, oxygen-enriched air and pure oxygen used as the oxidizer, and heat recovery systems in both CI and SI internal combustion engines. None of these patents use these elements in the same way as this invention.
The six stroke engine described in this invention has strokes two and four the same as other four or six stroke engines; however, strokes one, three, five, and six are different. The drawings and the descriptions that follow will clearly show those differences and the advantages of this six stroke engine over prior art.